1. Field of the Invention
The present invention generally relates to accessing data in a multiple processor system. More specifically, the present invention provides techniques for improving data access efficiency while maintaining cache coherency in a multiple processor system having a multiple cluster architecture.
2. Description of Related Art
Performance limitations have led to the development of a point-to-point architecture for connecting processors in a system with a single memory space. In one example, individual processors can be directly connected to each other through a plurality of point-to-point links to form a cluster of processors. Separate clusters of processors can also be connected. The point-to-point links significantly increase the bandwidth for coprocessing and multiprocessing functions.
Mechanisms are provided in each cluster to allow reduction in the number of transactions within and between clusters in a computer system. However, in many instances, the mechanisms do not optimally reduce the number of transactions. In a multiple processor, multiple cluster system, processors send probe requests in order to perform operations on particular memory lines that may be cached in local or remote nodes. Some common operations include read block, read block shared, and read block modified operations on memory lines. In many examples, transactions are forwarded to remote clusters even when transactions could be handled locally if additional mechanisms were provided. However, mechanisms for handling transactions locally are limited.
Consequently, it is desirable to provide techniques for improving cache access request efficiency in systems having multiple clusters of multiple processors connected using point-to-point links.